1,4-Cyclohexanedicarboxylic acid is useful as a starting material of medicinal drugs, synthetic resins, synthetic fibers, dyes, etc. In particular, in view of its heat resistance, electrical properties, and optical properties, there has recently been an increasing demand for high-purity 1,4-cyclohexanedicarboxylic acid as an acid component for polyester resins for the application of optical and electronic materials.
A commonly used method for preparing 1,4-cyclohexanedicarboxylic acid comprises hydrogenating the aromatic ring of the disodium salt of terephthalic acid in an aqueous solution to give the disodium salt of 1,4-cyclohexanedicarboxylic acid, followed by precipitation by addition of an acid, such as hydrochloric acid, sulfuric acid, or the like to give 1,4-cyclohexanedicarboxylic acid (Patent Literature (PTL) 1). However, 1,4-cyclohexanedicarboxylic acid prepared by this method contains metal such as sodium from the preparation method, as well as residual acid components containing chlorine, sulfur, etc., from the precipitation by acid addition, possibly posing problems such that the polymerization degree is not easily increased in polymers obtained by using the 1,4-cyclohexanedicarboxylic acid as a starting material; and that due to the residual acid components, there are concerns about metal corrosion in devices etc., or an effect on electrical properties of the devices etc.
Other known methods comprise directly performing nuclear hydrogenation of terephthalic acid (PTL 2, PTL 3, and PTL 4). All of these methods inevitably produce impurities of monocarboxylic acids as by-products, such as cyclohexanecarboxylic acid and 4-methylcyclohexanecarboxylic acid. Furthermore, the monocarboxylic acids as impurities cannot be easily separated by recrystallization or other commonly used methods. Therefore, in terms of polymers obtained by using, as a starting material, 1,4-cyclohexanedicarboxylic acid containing these impurities, there could be problems such that the polymerization degree is not easily increased; or that there are concerns about effects on properties such as heat resistance, weather resistance, and physical strength.
Additionally, a method has also been proposed for obtaining 1,4-cyclohexanedicarboxylic acid by subjecting dialkyl terephthalate to nuclear hydrogenation, and subjecting the resulting dialkyl 1,4-cyclohexanedicarboxylate to a hydrolysis reaction in an aqueous solution in the presence of an acid catalyst. In this method, at the time of hydrolysis, water is continuously or intermittently added to the reaction system while water and a by-product alcohol produced during the hydrolysis reaction are continuously evaporated out of the reaction system (PTL 5).
As described above, in general, for organic compounds, increasing purity and reducing the content of impurities could be primary problems to be solved. In terms of an organic compound in the form of a powder, an industrially important problem is whether the powder handleability is satisfactory. The powder handleability is mainly evaluated based on powder flowability and floodability. Depending on the degree of the powder flowability and floodability, installation of corresponding mechanical devices or an improvement in working environment etc. could be required, which is economically disadvantageous. Solving such problems is often not easy because even organic compounds with the same chemical structure have different powder properties due to the effects of, for example, their production history, storage history, and characteristic properties specific to the substance (stickiness, adhesion, etc.). That is, one of the factors that makes it more difficult to improve the powder handleability lies in the difficulty in identifying the cause of the effect on powder properties.